Compensation systems and methods for display OLED degradation

ABSTRACT

What is disclosed are systems and methods for compensating for display OLED degradation. Correction factors k for OLED degradation of each sub-pixel is modelled and tracked based on grey level, temperature, and time, and used to correct image data provided to an OLED display.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.62/700,415, filed Jul. 19, 2018, which is hereby incorporated byreference herein in its entirety.

FIELD OF THE INVENTION

The present disclosure relates to image correction for light emissivevisual display technology, and particularly to organic light emittingdevice (OLED) degradation compensation systems and methods forcorrecting images of active matrix organic light emitting diode device(AMOLED) displays.

BRIEF SUMMARY

According to a first aspect, there is provided a method for compensatingfor degradation of sub-pixels of an emissive display panel of a hostdevice, each sub-pixel having a light-emitting device, the methodcomprising: storing for each sub-pixel a correction factor representinga degradation of the sub-pixel in non-volatile memory; during operationof the display panel, sampling grey level data of the image data foreach sub-pixel, and temperature data corresponding to said sub-pixel;determining an updated correction factor for each sub-pixel as afunction of the sampled grey level data and temperature data for eachsub-pixel; and applying the correction factor for each sub-pixel to theimage data for the sub-pixel, generating corrected image data fordisplay by the emissive display panel.

Some embodiments further provide for storing the updated correctionfactor in the non-volatile memory. In some embodiments, the updatedcorrection factor is stored in the non-volatile memory each time theupdated correction factor is determined. In some embodiments, theupdated correction factor is stored in the non-volatile memoryimmediately prior to shut-down of the host device.

Some embodiments further provide for storing the updated correctionfactor for each sub-pixel in volatile memory. In some embodiments, theupdated correction factor for each sub-pixel is stored in a look-uptable in volatile memory.

In some embodiments, the updated correction factor for each sub-pixel isdetermined according to an OLED degradation model.

In some embodiments, the updated correction factor for each sub-pixel isfurther determined as a function of a sampling time period.

In some embodiments, the updated correction factor for each sub-pixel isdetermined as a sum of a product of a first function of the sampled greylevel data, a second function of a sampling time period, and a thirdfunction of the sampled temperature data of each sub-pixel.

In some embodiments, the updated correction factor for each sub-pixel isdetermined with use of a look-up table, the sampled grey level data, asampling time period, and the sampled temperature data.

According to another aspect there is provided a degradation compensationsystem for compensating for degradation of sub-pixels of an emissivedisplay panel of a host device, each sub-pixel having a light-emittingdevice, the system comprising: an image data block; a non-volatilememory; the emissive display panel; and a processing unit for: storingfor each sub-pixel a correction factor representing a degradation of thesub-pixel in non-volatile memory; during operation of the display panel,sampling grey level data of the image data received from the image blockfor each sub-pixel, and temperature data corresponding to said sub-pixelreceived from the emissive display panel; and determining an updatedcorrection factor for each sub-pixel as a function of the sampled greylevel data and temperature data for each sub-pixel; and a compensationblock for applying the correction factor for each sub-pixel to the imagedata for the sub-pixel received from the image data block, generatingcorrected image data for display by the emissive display panel.

In some embodiments, the non-volatile memory is further for storing theupdated correction factor. In some embodiments, the non-volatile memoryis further for storing the updated correction factor each time theupdated correction factor is determined. In some embodiments, thenon-volatile memory is further for storing the updated correction factorimmediately prior to shut-down of the host device.

Some embodiments further provide for a volatile memory for storing theupdated correction factor for each sub-pixel. In some embodiments, theupdated correction factor for each sub-pixel is stored in a look-uptable in volatile memory.

In some embodiments, the processing unit determines the updatedcorrection factor for each sub-pixel according to an OLED degradationmodel.

In some embodiments, the processing unit further determines the updatedcorrection factor for each sub-pixel as a function of a sampling timeperiod.

In some embodiments, the processing unit determines the updatedcorrection factor for each sub-pixel as a sum of a product of a firstfunction of the sampled grey level data, a second function of a samplingtime period, and a third function of the sampled temperature data ofeach sub-pixel.

In some embodiments, the processing unit determines the updatedcorrection factor for each sub-pixel with use of a look-up table, thesampled grey level data, a sampling time period, and the sampledtemperature data.

In some embodiments, wherein the processing unit comprises a graphicsprocessing unit (GPU) or a central processing unit (CPU) of the hostdevice.

The foregoing and additional aspects and embodiments of the presentdisclosure will be apparent to those of ordinary skill in the art inview of the detailed description of various embodiments and/or aspects,which is made with reference to the drawings, a brief description ofwhich is provided next.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other advantages of the disclosure will becomeapparent upon reading the following detailed description and uponreference to the drawings.

FIG. 1 illustrates an example display system which participates in andwhose pixels are corrected by the degradation compensation systems andmethods disclosed; and

FIG. 2 is a schematic block diagram of an OLED degradation compensationsystem in accordance with an embodiment.

While the present disclosure is susceptible to various modifications andalternative forms, specific embodiments or implementations have beenshown by way of example in the drawings and will be described in detailherein. It should be understood, however, that the disclosure is notintended to be limited to the particular forms disclosed. Rather, thedisclosure is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of an invention as defined by theappended claims.

DETAILED DESCRIPTION

An OLED device is a Light Emitting Diode (LED) in which the emissiveelectroluminescent layer is a film of organic compound that emits lightin response to an electric current. This layer of organic layers issituated between two electrodes; typically, at least one of theseelectrodes is transparent. Compared to conventional Liquid CrystalDisplays (LCDs), Active Matrix Organic Light Emitting Device (AMOLED)displays offer lower power consumption, manufacturing flexibility,faster response time, larger viewing angles, higher contrast, lighterweight and amenability to flexible substrates. An AMOLED display workswithout a backlight because it emits visible light and each pixelconsists of different colored OLEDs emitting light independently. TheOLED panel can display deep black level and can be thinner than an LCDdisplay.

Typically, LED and AMOLED displays require some form of image correctionpost fabrication. All LED and AMOLED displays, regardless of backplanetechnology, exhibit differences in luminance on a pixel to pixel basis,primarily as a result of process or construction inequalities, or fromaging caused by operational use over time. Luminance non-uniformities ina display may also arise from natural differences in chemistry andperformance from the LED and OLED materials themselves. Thesenon-uniformities must be managed by the LED and AMOLED displayelectronics in order for the display device to attain commerciallyacceptable levels of performance for mass-market use.

To facilitate image correction, for a given display aftersingularization, methods such In-Pixel Compensation (IPC) or electricalmeasurement or a combination of both IPC compensation and electricalmeasurement, may also be used to acquire the correction data. Thecorrection data is then stored on a Non-Volatile Memory (NVM) chipinside the display system and final product as initial correction datafor later processing and updating as and when further degradationoccurs.

While the embodiments described herein will be in the context of AMOLEDdisplays it should be understood that the degradation correction systemsand methods described herein are applicable to any other displaycomprising pixels which undergo degradation similar to that of OLEDsdescribed below.

It should be understood that the embodiments described herein pertain tosystems and methods of image correction and degradation compensation anddo not limit the display technology underlying their operation and theoperation of the displays in which they are implemented. The systems andmethods described herein are applicable to any number of various typesand implementations of various visual display technologies.

FIG. 1 is a diagram of an example display system 150 whose degradationis to be compensated and whose images are to be corrected with thesystems and methods described further below in conjunction with anarrangement with a compensation system 200 of FIG. 2. The display system150 includes a display panel 120, an address driver 108, a data driver104, a controller 102, and a memory storage 106.

The display panel 120 includes an array of pixels 110 (only oneexplicitly shown) arranged in rows and columns. Each of the pixels 110is individually programmable to emit light with individuallyprogrammable luminance values. The controller 102 receives digital dataindicative of information to be displayed on the display panel 120. Thecontroller 102 sends signals 132 to the data driver 104 and schedulingsignals 134 to the address driver 108 to drive the pixels 110 in thedisplay panel 120 to display the information indicated. The plurality ofpixels 110 of the display panel 120 thus comprise a display array ordisplay screen adapted to dynamically display information according tothe input digital data received by the controller 102. The displayscreen and various subsets of its pixels define “display areas” whichmay be used for monitoring and managing display brightness. The displayscreen can display images and streams of video information from datareceived by the controller 102. The supply voltage 114 provides aconstant power voltage or can serve as an adjustable voltage supply thatis controlled by signals from the controller 102. The display system 150can also incorporate features from a current source or sink (not shown)to provide biasing currents to the pixels 110 in the display panel 120to thereby decrease programming time for the pixels 110.

For illustrative purposes, only one pixel 110 is explicitly shown in thedisplay system 150 in FIG. 1. It is understood that the display system150 is implemented with a display screen that includes an array of aplurality of pixels, such as the pixel 110, and that the display screenis not limited to a particular number of rows and columns of pixels. Forexample, the display system 150 can be implemented with a display screenwith a number of rows and columns of pixels commonly available indisplays for mobile devices, monitor-based devices, and/orprojection-devices. In a multichannel or color display, a number ofdifferent types of pixels, each responsible for reproducing color of aparticular channel or color such as red, green, or blue, will be presentin the display. Pixels of this kind may also be referred to as“subpixels” as a group of them collectively provide a desired color at aparticular row and column of the display, which group of subpixels maycollectively also be referred to as a “pixel”.

The pixel 110 is operated by a driving circuit or pixel circuit thatgenerally includes a driving transistor and a light emitting device.Hereinafter the pixel 110 may refer to the pixel circuit. The lightemitting device can optionally be an organic light emitting diode, butimplementations of the present disclosure apply to pixel circuits havingother electroluminescence devices which may be subject to similardegradation, including current-driven light emitting devices. Thedriving transistor in the pixel 110 can optionally be an n-type orp-type amorphous silicon thin-film transistor, but implementations ofthe present disclosure are not limited to pixel circuits having aparticular polarity of transistor or only to pixel circuits havingthin-film transistors. The pixel circuit 110 can also include a storagecapacitor for storing programming information and allowing the pixelcircuit 110 to drive the light emitting device after being addressed.Thus, the display panel 120 can be an active matrix display array.

As illustrated in FIG. 1, the pixel 110 illustrated as the top-leftpixel in the display panel 120 is coupled to a select line 124, a supplyline 126, a data line 122, and a monitor line 128. A read line may alsobe included for controlling connections to the monitor line. In oneimplementation, the supply voltage 114 can also provide a second supplyline to the pixel 110. For example, each pixel can be coupled to a firstsupply line 126 charged with Vdd and a second supply line 127 coupledwith Vss, and the pixel circuits 110 can be situated between the firstand second supply lines to facilitate driving current between the twosupply lines during an emission phase of the pixel circuit. It is to beunderstood that each of the pixels 110 in the pixel array of the displaypanel 120 is coupled to appropriate select lines, supply lines, datalines, and monitor lines. It is noted that aspects of the presentdisclosure apply to pixels having additional connections, such asconnections to additional select lines, and to pixels having fewerconnections.

With reference to the pixel 110 of the display panel 120, the selectline 124 is provided by the address driver 108, and can be utilized toenable, for example, a programming operation of the pixel 110 byactivating a switch or transistor to allow the data line 122 to programthe pixel 110. The data line 122 conveys programming information fromthe data driver 104 to the pixel 110. For example, the data line 122 canbe utilized to apply a programming voltage or a programming current tothe pixel 110 in order to program the pixel 110 to emit a desired amountof luminance. The programming voltage (or programming current) suppliedby the data driver 104 via the data line 122 is a voltage (or current)appropriate to cause the pixel 110 to emit light with a desired amountof luminance according to the digital data received by the controller102. The programming voltage (or programming current) can be applied tothe pixel 110 during a programming operation of the pixel 110 so as tocharge a storage device within the pixel 110, such as a storagecapacitor, thereby enabling the pixel 110 to emit light with the desiredamount of luminance during an emission operation following theprogramming operation. For example, the storage device in the pixel 110can be charged during a programming operation to apply a voltage to oneor more of a gate or a source terminal of the driving transistor duringthe emission operation, thereby causing the driving transistor to conveythe driving current through the light emitting device according to thevoltage stored on the storage device.

Generally, in the pixel 110, the driving current that is conveyedthrough the light emitting device by the driving transistor during theemission operation of the pixel 110 is a current that is supplied by thefirst supply line 126 and is drained to a second supply line 127. Thefirst supply line 126 and the second supply line 127 are coupled to thesupply voltage 114. The first supply line 126 can provide a positivesupply voltage (e.g., the voltage commonly referred to in circuit designas “Vdd”) and the second supply line 127 can provide a negative supplyvoltage (e.g., the voltage commonly referred to in circuit design as“Vss”). Implementations of the present disclosure can be realized whereone or the other of the supply lines (e.g., the supply line 127) isfixed at a ground voltage or at another reference voltage.

The display system 150 also includes a monitoring system 112. Withreference again to the pixel 110 of the display panel 120, the monitorline 128 connects the pixel 110 to the monitoring system 112. Themonitoring system 12 can be integrated with the data driver 104, or canbe a separate stand-alone system. In particular, the monitoring system112 can optionally be implemented by monitoring the current and/orvoltage of the data line 122 during a monitoring operation of the pixel110, and the monitor line 128 can be entirely omitted. The monitor line128 allows the monitoring system 112 to measure a current or voltageassociated with the pixel 110 and thereby extract information indicativeof a degradation or aging of the pixel 110 or indicative of atemperature of the pixel 110. In some embodiments, display panel 120includes temperature sensing circuitry devoted to sensing temperatureimplemented in the pixels 110. In some embodiments the temperaturesensing circuitry of the display panel 120 measures temperature on apixel-by-pixel basis, while in others it determines coarse localtemperatures for a number of display areas, while in others, itdetermines a single global temperature of the display panel 120. Inother embodiments, the pixels 110 comprise circuitry which participatesin both sensing temperature and driving the pixels. For example, themonitoring system 112 can extract, via the monitor line 128, a currentflowing through the driving transistor within the pixel 110 and therebydetermine, based on the measured current and based on the voltagesapplied to the driving transistor during the measurement, a thresholdvoltage of the driving transistor or a shift thereof.

The controller 102 and memory 106 together or also in combination with acorrection block (not shown in FIG. 1) use compensation data orcorrection data, in order to address and correct for the variousdefects, variations, and non-uniformities, existing at the time offabrication, and defects suffered further from aging and deteriorationafter usage. In some embodiments, the correction data includes data forcorrecting the luminance of the pixels obtained through OLED degradationtracking and modelling using a compensation system as described below,while in other embodiments OLED degradation is applied to the image dataprior to its being provided in memory 106. Some embodiments employ themonitoring system 112 to characterize the behavior of the pixels and tocontinue to monitor aging and deterioration as the display ages and toupdate the correction data to compensate for said aging anddeterioration over time. Some embodiments the combine compensationperformed by the monitoring system 112 and the controller 102 with thedegradation compensation performed by the compensation system 200described below while in others embodiments only the compensation system200 performs any degradation compensation.

Referring to FIG. 2, a compensation system 200 for display degradationaccording to an embodiment will now be described.

The compensation system 200 includes the OLED display 210 which is to becorrected, and a central or graphics processing unit 216, as well as animage data block 212 which generates or receives the images to bedisplayed, and a non-volatile memory (NVM) 214 such as NAND flashmemory. NVM 214 may be implemented in the non-volatile memory of a hostdevice, in which the correction system 200 is implemented. The centralor graphics processing unit 216 can comprise, for example, a CPU or aGPU of the host device or system in which the OLED display 210 isimplemented. Such a host device or system could be, for example, amobile device, phone, laptop, tablet, desktop, or TV. In another case,the processing unit 216 can be part of the display system and/or thecontroller 102 illustrated in FIG. 1, for example, integrated in atiming controller TCON. In some implementations, the OLED display 210 ofFIG. 2 may correspond more or less to the display system 150 of FIG. 1and includes similar components thereof. In some embodiments, theprocessing unit 216 is external to the display system 150 illustrated inFIG. 1 and provides corrected image data 244 to memory 107 as the imagedata referred to hereinabove with respect to FIG. 1.

The processing unit 260 includes SRAM memory 220 as well as a number offunctional blocks which may be implemented with software, firmware, orspecialized hardware of the processing unit 260. These include a sampler226, a correction block 218, and a correction factor determination unit221 which includes a correction factor lookup unit 224 and a correctionfactor calculation unit 222. As illustrated in FIG. 2, each of thefunctional blocks of the processing unit 216 have access to SRAM 220 forstoring and retrieving any of the data utilized in the compensationprocess, as and when needed.

Image data 230 which is generated or received at the image data block212 and comprise images intended for display on the OLED display 210,are processed by the correction block 218 of the processing unit 216utilizing correction factors 238 (described below) to generate correctedimage data 244 for display by the OLED display 210. The corrected imagedata 244 compensates for OLED degradation of the sub-pixels of the OLEDdisplay 210.

Correction factors k for each sub-pixel of the OLED display 210 arestored in persistent storage such as non-volatile memory 214 in order tokeep record of the degradation of the OLED display 210 over successivepower up and shut down of the host device or system in which thecompensation system 200 is implemented. In some embodiments, correctionfactors k are stored for each and every subpixel in a lookup table. Thislookup table is stored in SRAM 220 of the processing unit 216 while thecorrection system 200 is in operation, and is also stored in the NVM 214for persistent storage while correction system 200 is powered down. Onpower-up, the previously stored correction factors k are loaded from theNVM 214 to the SRAM 220 as starting k values which are periodicallyupdated. In some embodiments, the device or system starts withcorrection factors k prepopulated from the factory in the NVM 214.

In order to track OLED degradation of each sub-pixel of the OLED display210 in accordance with the model described below, while in operation,and sampler 226 of the processing unit 216 periodically samples greyscale or grey level data of the image data 230 from the image data block212 intended for the sub-pixels of the OLED display 210. The sampler 226also has access to temperature data (T) 234 originating from the OLEDdisplay 210 which it periodically samples. In some embodiments, thistemperature data is provided for each and every subpixel, while in otherembodiments the same temperature data (T) 226 applies to a plurality ofthe sub-pixels in each display area or, in the case where thetemperature data (T) 234 is a single global temperature, applies to allof the sub-pixels. The sampler 226 provides sampled grey level andtemperature data (sampled data 246) to the correction factordetermination unit 221 which performs the necessary calculations togenerate the correction factor k including integration or summationaccording to the model described below.

Once provided with the sampled data 248, the correction factorcalculation unit 222 calculates the new correction factor k by obtainingthe currently stored k factor and adding to it according to the model.As described below, the calculation of the new correction factor kdepends upon the grey level data (GL), temperature data (T), and time(t), the last of which the correction factor calculation unit hasindependent access to. In some embodiments, the currently stored kfactor for a particular sub-pixel is obtained from the look up table inSRAM 220 using the correction factor look-up unit 224. Once the newcorrection factor k is determined it is stored in SRAM 220, and alsostored in NVM 214. In some embodiments, any updates to the correctionfactors in SRAM 220 is mirrored in the NVM 214 in order to keep thepersistent correction factors current. In other embodiments the NVM 214is updated with the current correction factors in SRAM 220 immediatelyprior to the host device or system being powered down.

The correction block 218 utilizes the correction factors k for everysub-pixel in its correction of the image data 230 into corrected imagedata 244 provided to the OLED display 210. In some embodiments thecorrection block 218 utilizes the correction factor look-up unit 224 tofetch the current correction factor k 218 for the sub-pixel whose datait is currently correcting. In other embodiments, the current correctionfactors are directly obtained from SRAM 220.

In some embodiments the correction unit 216 utilizes the correctionfactor multiplicatively to generate the corrected image data 244. Insome embodiments the corrected grey level for each sub-pixel in thecorrected image data 244 is generated by the correction unit 216, bymultiplying the original grey level for each sub-pixel in the image data230 by a function of the corresponding correction factor k of thesub-pixel. In some embodiments this function is non-linear.

In some embodiments, the correction factor look-up unit 224 includesfunctionality to look-up additional look-up tables for optimizing thecalculation of the correction factors according to the model. In theseembodiments, the functional dependence of the correction factor k uponthe sampled data (grey level GL, temperature T, as well as time t) arestored in a look-up table to reduce processing computation of thecorrection factors k. In such an embodiment, the correction factorcalculation unit 222 uses the correction factor look-up unit and thesampled grey level and temperature data, and its own tracking of time,to fetch the values of F₁, F₂, and F₃ (see below) from which itcalculates the value of correction factor k, or to directly fetch thecorrection factor k.

In some embodiments, the frequency of access of the correction factors kby the correction block 218 exceeds the frequency of calculation andupdate of the correction factors k by the sampler 226 working in tandemwith the correction factor determination unit 221. In such embodiments,the correction block 218 accesses the current correction factor k eachtime it is needed independently of when the correction factors areupdated by the correction factor determination unit 221.

The correction factor determination unit 221 determines the correctionfactor k, according to an OLED degradation correction model in which thecorrection factor k is proportional to the overall sum of stress energythat an OLED endures during the time period from t_(i) to t_(n) asfollows:k∝E _(OLED)  (1)

Here, the OLED energy E_(OLED) is the accumulation of the product of theOLED voltage, V_(OLED), and the OLED driving current, I_(OLED):E _(OLED)=∫_(t) _(i) ^(t) ^(n) P _(OLED)(t)dt=∫ _(t) _(i) ^(t) ^(n) (I_(OLED)(t)×V _(OLED)(t,T))dt  (2)

As illustrated in formula (2), P_(OLED) represents the instantaneouspower of the OLED and T represents the operating temperature of theOLED.

The OLED voltage V_(OLED) can vary during the period as can themagnitude of the driving current I_(OLED). An empirical model ofequation (2) is provided such that the correction factor k isproportional to the accumulated stress Grey Level (GL) and time withmathematical functions as follows:k∝F(GL,t,T)  (3)k∝ΣF ₁(GL)×F ₂(t)×F ₃(T)  (4)

Where, F₁(GL), F₂ (t) and F₃ (T) represent the function of OLED drivingcurrent, the function of time and the function of temperature in whichan OLED is operating respectively. In some embodiments, F₁(GL) is of theform A*(GL)^(γ), for example, where γ is the intensity gamma curve forthe OLED display, while in others F₁(GL) is a polynomial of GL. In someembodiments, F₂ (t) is a polynomial of t. In some embodiments, F₃ (T) isof the form C*T/T₀, in others a polynomial of T, and in others apolynomial of [−C*exp(1/T−1/T₀)] where T₀ is a predetermined referencetemperature.

In embodiments which utilize a look-up table for computation of thecorrection factor k or each of F₁, F₂, and F₃, the correction factorcalculation unit 222 utilizes the correction factor look-up unit 224 tofetch the relevant value using GL, t, and T In other embodiments, thevalue of k is computed by integration or summation along withcalculations of the product of the appropriate functional forms of F₁,F₂, and F₃.

Although the algorithms or processes described above have been describedseparately, it should be understood that any two or more of thealgorithms or processes disclosed herein can be combined in anycombination. Any of the methods, algorithms, implementations, orprocedures described herein can include machine-readable instructionsfor execution by: (a) a processor, (b) a controller, and/or (c) anyother suitable processing device. Any algorithm, software, or methoddisclosed herein can be embodied in software stored on a non-transitorytangible medium such as, for example, a flash memory, a CD-ROM, a floppydisk, a hard drive, a digital versatile disk (DVD), or other memorydevices, but persons of ordinary skill in the art will readilyappreciate that the entire algorithm and/or parts thereof couldalternatively be executed by a device other than a controller and/orembodied in firmware or dedicated hardware in a well-known manner (e.g.,it may be implemented by an application specific integrated circuit(ASIC), a programmable logic device (PLD), a field programmable logicdevice (FPLD), discrete logic, etc.). Also, some or all of themachine-readable instructions represented in process described hereincan be implemented manually as opposed to automatically by a controller,processor, or similar computing device or machine. Further, althoughspecific algorithms or processes have been described, persons ofordinary skill in the art will readily appreciate that many othermethods of implementing the example machine readable instructions mayalternatively be used. For example, the order of execution of the stepsmay be changed, and/or some of the blocks described may be changed,eliminated, or combined.

It should be noted that the algorithms illustrated and discussed hereinas having various modules which perform particular functions andinteract with one another. It should be understood that these modulesare merely segregated based on their function for the sake ofdescription and represent computer hardware and/or executable softwarecode which is stored on a computer-readable medium for execution onappropriate computing hardware. The various functions of the differentmodules and units can be combined or segregated as hardware and/orsoftware stored on a non-transitory computer-readable medium as above asmodules in any manner, and can be used separately or in combination.

While particular implementations and applications of the presentdisclosure have been illustrated and described, it is to be understoodthat the present disclosure is not limited to the precise constructionand compositions disclosed herein and that various modifications,changes, and variations can be apparent from the foregoing descriptionswithout departing from the spirit and scope of an invention as definedin the appended claims.

What is claimed is:
 1. A method for compensating for degradation ofsub-pixels of an emissive display panel of a host device, the hostdevice also including an image data block configured to generate orreceive image data, including grey level data, for displaying images onthe emissive display panel, each sub-pixel comprising a light-emittingdevice, the method comprising: storing for each sub-pixel a correctionfactor representing a degradation of the sub-pixel in non-volatilememory; during operation of the emissive display panel, sampling thegrey level data of the image data via the image data block intended forat least one sub-pixel prior to being provided to the emissive displaypanel generating sampled grey level data; and sampling temperature datacorresponding to said at least one sub-pixel; determining an updatedcorrection factor for each of the at least one sub-pixel as a functionof the sampled grey level data and the temperature data corresponding tosaid at least one sub-pixel; and applying the updated correction factorfor each of the at least one sub-pixel to the image data for the atleast one sub-pixel, generating corrected image data for display by theemissive display panel.
 2. The method of claim 1, further comprisingstoring each updated correction factor in the non-volatile memory in thehost device.
 3. The method of claim 2, wherein each updated correctionfactor is stored in the non-volatile memory each time each updatedcorrection factor is determined.
 4. The method of claim 2, wherein eachupdated correction factor is stored in the non-volatile memoryimmediately prior to shut-down of the host device.
 5. The method ofclaim 1, further comprising storing each updated correction factor involatile memory in the host device.
 6. The method of claim 5, whereineach updated correction factor is stored in a look-up table in thevolatile memory.
 7. The method of claim 1, wherein each updatedcorrection factor is determined according to an OLED degradation model.8. The method of claim 1, wherein each updated correction factor isfurther determined as a function of a sampling time period.
 9. Themethod of claim 1, wherein the updated correction factor for each of theat least one sub-pixel is determined as a sum of a product of a firstfunction of the sampled grey level data, a second function of a samplingtime period, and a third function of the temperature data correspondingto said at least one sub-pixel.
 10. The method of claim 1, wherein eachupdated correction factor is determined with use of a look-up table, thesampled grey level data, a sampling time period, and the temperaturedata corresponding to said at least one sub-pixel.
 11. A degradationcompensation system for compensating for degradation of sub-pixels of anemissive display panel of a host device, each sub-pixel including alight-emitting device, the system comprising: an image data blockconfigured to generate or receive image data, including grey level data,for displaying images on the emissive display panel; a non-volatilememory; the emissive display panel; and a processing unit for: storingfor each sub-pixel a correction factor representing a degradation of thesub-pixel in non-volatile memory; during operation of the display panel,sampling the grey level data of the image data received from the imageblock intended for at least one sub-pixel prior to being provided to theemissive display panel generating sampled grey level data, and samplingtemperature data corresponding to said at least one sub-pixel receivedfrom the emissive display panel; and determining an updated correctionfactor for each of the at least one sub-pixel as a function of thesampled grey level data and the temperature data for each of the atleast one sub-pixel; and a compensation block for applying the updatedcorrection factor for each of the at least one sub-pixel to the imagedata for the at least one sub-pixel received from the image data block,generating corrected image data for display by the emissive displaypanel.
 12. The system of claim 11, wherein the non-volatile memory isfurther for storing each updated correction factor.
 13. The system ofclaim 12, wherein the non-volatile memory is further for storing eachupdated correction factor each time each updated correction factor isdetermined.
 14. The system of claim 12, wherein the non-volatile memoryis further for storing each updated correction factor immediately priorto shut-down of the host device.
 15. The system of claim 11, furthercomprising volatile memory for storing each updated correction factor.16. The system of claim 15, wherein each updated correction factor isstored in a look-up table in volatile memory.
 17. The system of claim11, wherein the processing unit determines each updated correctionfactor according to an OLED degradation model.
 18. The system of claim11, wherein the processing unit further determines each updatedcorrection factor as a function of a sampling time period.
 19. Thesystem of claim 11, wherein the processing unit determines each updatedcorrection factor as a sum of a product of a first function of thesampled grey level data, a second function of a sampling time period,and a third function of the temperature data of each of the at least onesub-pixel.
 20. The system of claim 11, wherein the processing unitdetermines each updated correction factor with use of a look-up table,the sampled grey level data, a sampling time period, and the temperaturedata for each of the at least one sub-pixel.
 21. The system of claim 11,wherein the processing unit comprises a graphics processing unit (GPU)or a central processing unit (CPU) of the host device.